The invention relates to a method for joining tubing, fittings and valves of different standard diameter types.
For the purposes of the invention description presented herein, "CT" will be used to represent "standard water tube" size copper and copper alloy tubing, and "IP" will be used to represent "standard outside diameter" size steel pipe. In addition, the terms "tubing" and "pipe" are considered to be interchangeable, and reference to "copper tubing" will also be taken as referring to "copper alloy tubing" as an alternative.
A grooved end pipe coupling, e.g. of the type illustrated in FIG. 1, is used for joining together piping elements, e.g. tubing, fittings, valves, etc., in a leak tight assembly by use of grooves that are cut, cast or formed in the ends of the piping elements. Referring to FIGS. 2 and 3, critical parameters of a grooved end connection include: the gasket seat diameter, D.sub.s, groove diameter, D.sub.g, gasket seat width, W.sub.s, and groove width, W.sub.g. In the case of wrought metal piping elements, e.g., as above, tubing, fittings or valve bodies, the grooved end of the piping element, P, is conventionally produced by either a machining (cut) operation or a rolling (formed) operation as shown in piping element, P.sub.cut, of FIG. 2, and piping element P.sub.roll, of FIG. 3, respectively. In the case of a cast fitting or valve body, the grooved end connection is normally either cut in the configuration of a piping element, P.sub.cut shown in FIG. 2, or cast in the dual outward step configuration of a piping element, P.sub.cast, shown in FIG. 4.
Referring again to FIG. 1, a typical grooved end pipe coupling 10 consists of two or more housing segments 12, 14, a gasket 16, and fastening means, e.g. nuts 18 and bolts 20 for securing the assembly together with the end connections to be joined. The housing segments have keys 22 around the inner periphery at both ends, a shoulder 24 also around and just inside of each key, and a gasket cavity 26. The keys fit into the grooves 30 to axially and transversely retain the end connections. The keys and shoulders are involved to varying degrees in maintaining the coupling assembly generally centered about the grooved end connection. The shoulder fits closely around the gasket seat diameter to prevent the gasket from extruding outwardly under the internal pressure of the piping system, the gasket being retained in the gasket cavity and producing a seal on the gasket seat surfaces to form a leak tight assembly.
Traditionally, copper tubing has been joined by soldering or brazing. However, recent emphasis on use of lead free solder has considerably increased the difficulty of producing a soldered, leak free joint, especially in the 3 inch and above tubing diameter sizes. This has increased the potential cost effectiveness of using grooved end pipe couplings in copper tubing system construction.
Until now, grooved end pipe couplings for joining copper piping elements (tubing, fittings, valves, etc.) have typically been available only in couplings specifically designed to accommodate CT size wrought copper tubing, which has average outside diameters that are slightly less than those for the same nominal IP size steel pipe (as detailed, e.g., in the publication "The Copper Connection" by The Victaulic Company of America). By way of example only, a 4-inch nominal CT size copper tube has an average outside diameter ("OD") of 4.125 inches, while 4-inch nominal IP size steel pipe has an average outside diameter of 4.500 inches.
In addition to the use of specifically designed grooved end pipe couplings, however, within the present state of the art, other means have been employed to join tubing with an average outside diameter smaller than the actual diameter of an IP size steel pipe of the same nominal diameter. For example, a specially designed ring with an average outside diameter equivalent to that of IP size pipe may be secured in a sealed arrangement to the end of a tube having a smaller average outside diameter, or the average outside diameter of the pipe can be increased to that of IP size pipe through the use of a ring secured in a sealed arrangement around the ends of lower average diameter pipe. These approaches would be similar to the Type A through E pipe end ring concepts shown in AWWA Standard C-606 for Grooved and Shouldered Joints.
Also, it has been known to expand the end of a pipe (roll forming), although the published objectives of this process have been to either expand the ends of IP size grooved end steel pipe to eliminate the reduced wall thickness of machined (cut) groove joints, or to eliminate the protrusion 32 inside the pipe which is associated with conventional roll grooving as shown in FIG. 3, and described in Table A, below.
Prior art concerning roll grooving of copper tubing is also described in the brochure "The Copper Connection", by Victaulic Company of America, with respect to their specially designed copper connections. These grooved end couplings are of the same basic concept or design as grooved end pipe couplings for IP size steel pipe; however, the dimensions of the couplings have been dimensionally altered to accommodate the smaller average outside diameter dimensions for copper tubing.
TABLE A ______________________________________ Roll Groove Dimensions for Steel Pipe (Inches) NOMINAL W.sub.s W.sub.g D.sub.g D.sub.s ______________________________________ 2 .625 .344 2.250-.015 2.375 2-1/2 .625 .344 2.720-.018 2.875 3 .625 .344 3.344-.018 3.500 4 .625 .344 4.344-.020 4.500 5 .625 .344 5.395-.022 5.562 6 .625 .344 6.455-.022 6.625 ______________________________________ Tolerances: W.sub.s, W.sub.g = .+-..030 D.sub.g = +.000 D.sub.s = See OD tolerance in Table I (below).
Standard roll grooving reduces the internal diameter of the tubing at the roll groove and thereby increases the restriction to the fluid flow stream. This somewhat impedes fluid flow through the pipe and also creates an area for possible damage when used in abrasive media service. This process is also described in literature for the Victaulic Company of America Style 24 expanded pipe coupling, which is used to expand carbon steel pipe in abrasive service where the radially inward indentation created by standard roll grooving would be subject to excessive abrasion. This process, however, forms only the pipe end shoulder.